When an eNB transmits a specific signal known to both the eNB and a UE through a downlink channel in order to check downlink channel state, the UE can estimate the downlink channel state through the specific signal and feed back the estimation result to the eNB. This specific signal is referred to as a reference signal (RS) and a reference signal for measuring/estimating a channel may be referred to as a channel state information-reference signal (CSI-RS).
In conventional wireless communication systems, a single CSI-RS configuration is provided to a UE and the same parameter value is applied to all CSI-RS ports included in the CSI-RS configuration.
In enhanced wireless communication systems which need to support multi-cell coordinated transmission and/or improved inter-cell interference coordination, CSI-RSs from a plurality of transmission points may be transmitted to a single UE and subframes may have different interference characteristics. Accordingly, when CSI-RS configurations and CSI feedback schemes, defined in the conventional wireless communication systems, are applied to the enhanced wireless communication systems, a UE cannot correctly perform CSI feedback or cannot report a correct channel state. Therefore, there is need for a new method for performing CSI feedback correctly and efficiently in enhanced wireless communication systems.